1. Field of the Invention
The invention relates to methods, systems and structures for modifying ice adhesion strength between ice and selected objects. More particularly, the invention relates to methods, systems and structures that apply electrical energy to the interface between ice and objects so as to either increase or decrease the ice adhesion strength to facilitate desired results.
2. Statement of the Problem
Ice adhesion to certain surfaces causes many problems. For example, excessive ice accumulation on aircraft wings endangers the plane and its passengers. Ice on ship hulls creates navigational difficulties, the expenditure of additional power to navigate through water and ice, and certain unsafe conditions. The need to scrape ice that forms on automobile windshields is regarded by most adults as a bothersome and recurring chore; and any residual ice risks driver visibility and safety.
Icing and ice adhesion also causes problems with helicopter blades, and with public roads. Billions of dollars are spent on ice and snow removal and control. Ice also adheres to metals, plastics, glasses and ceramics, creating other day-to-day difficulties. Icing on power lines is also problematic. Icing adds weight to the power lines which causes power outages, costing billions of dollars in direct and indirect costs.
In the prior art, methods for dealing with ice adhesion vary, though most techniques involve some form of scraping, melting or breaking. For example, the aircraft industry utilizes a deicing solution such as ethyl glycol to douse aircraft wings so as to melt the ice thereon. This process is both costly and environmentally hazardous; however, the risk to passenger safety warrants its use. Other aircraft utilize a rubber tube aligned along the front of the aircraft wing, whereby the tube is periodically inflated to break any ice disposed thereon. Still other aircraft redirect jet engine heat onto the wing so as to melt the ice.
These prior art methods have limitations and difficulties. First, prop-propelled aircraft do not have jet engines. Secondly, rubber tubing on the front of aircraft wings is not aerodynamically efficient. Third, de-icing costs are extremely high, at $2500-$3500 per application; and it can be applied up to about ten times per day on some aircraft. With respect to other types of objects, heating ice and snow is common. But, heating of some objects is technically impractical. Also, large energy expenditures and complex heating apparati often make heating too expensive.
The above-referenced problems generally derive from the propensity of ice to form on and stick to surfaces. However, ice also creates difficulties in that it has an extremely low coefficient of friction. Each year, for example, ice on the roadway causes numerous automobile accidents, costing both human life and extensive property damage. If automobile tires gripped ice more efficiently, there would likely be fewer accidents.
U.S. Pat. No. 6,027,075, incorporated herein by reference, discloses certain embodiments of an invention in which electrical energy in the form of a direct current (xe2x80x9cDCxe2x80x9d) bias is applied to the interface between ice and the object that the ice covers. As a result, the ice adhesion strength of the ice to the surface of the object is modified. Typically, the ice adhesion strength is decreased, making it possible to remove ice from the object by wind pressure, buffeting or light manual brushing. In other applications, the ice adhesion strength between ice and surfaces of objects in contact with the ice are increased. For example, when the ice adhesion strength is increased between automobile tires and icy roadways, there is less slippage and fewer accidents. In general, if a charge is generated at the interface of ice in contact with a object, it is possible to selectively modify the adhesion between the ice and the object.
In general, U.S. Pat. No. 6,027,075 discloses a power source connected to apply a DC voltage across the interface between ice and the surface upon which the ice forms. By way of example, the object having the conductive surface can be an aircraft wing or a ship""s hull (or even the paint applied to the structure). U.S. Pat. No. 6,027,075 discloses a first electrode connected with the surface; a nonconductive or electrically insulating material is applied as a grid over the surface; and a second electrode is formed by applying a conductive material, for example conductive paint, over the insulating material, but without contacting the surface. A practical problem, however, with the grid electrode system disclosed in U.S. Pat. No. 6,027,075 is formation of the grid electrodes and associated insulating layers. The individual components of the grid system, including electrodes, wiring and insulators, are fabricated on a small scale. Photolithographic techniques are capable of fabricating such grid systems. Photolithography is used very effectively in integrated circuit fabrication. The use of photolithography to form a grid system for modifying ice adhesion, however, is less suitable. It involves a large number of patterning and etching steps. Applied to ice control technology, photolithography is expensive, complicated and unreliable.
The present invention replaces the grid described in U.S. Pat. No. 6,027,075. An embodiment of the present invention provides a composite coating comprising separate, closely spaced wire electrodes separated by insulator fibers. The wire electrodes and insulator fibers are typically woven together using known and reliable industrial technologies. The wire electrodes are connected alternately to a DC power source in such a manner to function as cathodes and anodes. The composite coating is durable and flexible, and is typically applied to the surface to be protected using conventional adhesives. The metal wires may be gold, platinum-plated titanium or niobium, or other material with high resistance to electro-corrosion. As dielectric insulator fibers, nylon, glass or other dielectric material may be used. The dielectric fibers keep the metal electrodes apart, while providing coating integrity. In addition, the dielectric insulator fibers electrically insulate the wire electrodes from the surface on which the composite coating is applied. Typical wire diameters are in the range of from 10 to 100 xcexcm, with the same range of open space between the electrode wires and insulator fibers. If ice forms in and over the composite coating, a dc bias is applied to the electrodes. As a result, the ice adhesion strength at the interface of the ice and the surface of the object being protected is modified.
In another embodiment of the invention, the wire electrodes of a composite coating are connected to a DC bias source so that they have the same DC bias. The surface on which the composite coating is applied is electrically conductive and has an opposite DC bias. Ice formed in the spaces of the composite coating close the electrical circuit.
In another embodiment of the invention, a wire mesh comprising electrically conductive wires is formed. The wire mesh is disposed on an electrically conductive surface, with an insulating layer interposed between the wire mesh and the surface. A DC bias is applied to the wire mesh and an opposite DC bias is applied to the surface. Ice that is formed in the spaces of the wire mesh closes the electrical circuit.
Those skilled in the art should appreciate that the above-described system can be applied to surfaces of many objects where it is desired to reduce ice adhesion strength, such as on car windshields, airplane wings, ship hulls and power lines. When the invention takes the form of a composite cloth, it contains both the functional anodes and cathodes necessary for the system to work. Therefore, it is not important whether the surface of the object to be protected is electrically conductive or nonconductive.
The invention is next described further in connection with preferred embodiments, and it will become apparent that various additions, subtractions, and modifications can be made by those skilled in the art without departing from the scope of the invention.